java - 从数组列表打印

Question

我需要能够从数组列表中打印出所有有贷款的学生。

指金额大于 0 的所有学生。

我已经可以打印所有学生以及他们拥有多少钱..但我不知道如何让它只打印有贷款的学生。

这是当前代码

public class LoanCompany
{
    private ArrayList<StudentLoan> loans;
    /**
     * Constructor for objects of class LoanCompany
     */
    public LoanCompany()
    {
        loans = new ArrayList<StudentLoan>();
    }
    /**
     * add a loan amount and ID.
     */
    public void addLoan(String ID,int Amount) 
    { 
        StudentLoan newSLoan= new StudentLoan(ID,Amount);
        loans.add(newSLoan); 
    }
    /**
     * Return amount of loans
     */
    public int getNumberOfLoans()
    {
        return loans.size();
    }
    public void printLoanDitails()
    {
        System.out.println("Loan Summery: ");
        int index=0;
        for(StudentLoan loan : loans) {
            System.out.print(index + " : ");
            loan.printDetails();
            index++;
        }
        System.out.println();
    }
    /**
     * Remove index.
     */
    public void removeLoan(int index)
    {
        if(validIndex(index)) {
            loans.remove(index);
        }
    }
    /**
     * Valid index... validates the index.
     */
   private boolean validIndex(int index)
    {
        boolean valid;        
        if(index < 0) {
            System.out.println("Index must be 0 or a positive number");
            valid = false;
        }
        else if(index >= loans.size()) {
            System.out.println("Index is too large.");
            valid = false;
        }
        else {
            valid = true;
        }
        return valid;
    }
    /**
     * PayOff method, pays off the student loan.
     */
    public void payOff(int index, int Amount)
    {
        if(validIndex(index)) {
            StudentLoan student = loans.get(index);
            student.payOff(Amount);
            }
            else {
                System.out.println("Invalid Index.");
            }
     }
     /**
     * Prints outstanding loans.
     */
    public void printOutstandingLoans()
    {
        System.out.println("Loan Summery: ");
        for(StudentLoan loan : loans ) {
            int index=0;
            if (loan.getAmount() > 0) {
            System.out.print(index + " : ");
            loan.printDetails();
            index++;
            }           
        }
        System.out.println();
    }
    public void removeClearedLoans() {
       for(StudentLoan loan : loans ) {
           int index=0;
        if (loan.getAmount() == 0) {
            loans.remove(loan);
             System.out.print( "Cleared Loans Removed ");
            }
            index++;
        }
    }
}

Answer 1

我假设 StudentLoan 有一个字段 public int LoanAmount 那么你可以这样做:

for(StudentLoan loan : loans) {
        int index=0;
        if (loans.loanAmount > 0) {
            System.out.print(index + " : ");
            loan.printDetails();
            index++;
        }
    }

这样，只会打印 loanAmount > 0 的贷款。

如果字段 loanAmount 为 private，您只需为该字段实现一个 getter 方法并将条件更改为:

if (loan.getloanAmount() > 0) {

编辑

回答评论中的问题:

要删除 loamAmount 为 0 的所有贷款，我们只需向 foreach 循环添加另一个 if 即可:

for(StudentLoan loan : loans) {
        int index=0;

        // print loans with amount > 0

        if (loan.loanAmount > 0) {
            System.out.print(index + " : ");
            loan.printDetails();
            index++;
        }

        // delete loans with amount = 0

        if (loan.loanAmount == 0) {
           loans.remove(loan) // UNSAFE! see edit below
        }
    }

编辑

在迭代集合时使用 .remove 是不安全的。应该使用迭代器来完成，如下所示:

import java.util.Iterator // add to imports

Iterator<StudentLoan> i = loans.iterator();

while (i.hasNext()) {
    StudentLoan loan = i.next();
    if (loan.getAmount() == 0) {
        i.remove();
    }
}